In Bash, you can’t store the NULL-character in a variable.
You may, however, store a plain hex dump of the data (and later reverse this operation again) by using the xxd
command.
VAR1=`echo -ne "n\0m\0k" | xxd -p | tr -d '\n'`
echo -ne "$VAR1" | xxd -r -p | od -c # -> 0000000 n \0 m \0 k